新型双通道差分偏振干涉成像系统

针对Wollaston棱镜和Savart偏光镜(SP)组合的差分成像光谱系统存在光线溢出和无法改变系统光程等问题,设计了一种新型双通道差分偏振干涉成像系统.此系统不仅可获取正交偏振图像,还可以通过调整Savart偏光镜的厚度来改变系统光程.介绍了该系统的结构、理论原理,并利用琼斯矩阵推导出四束偏振光线的复振幅及其相干光干涉强度表达式.分析了宽视场Savart偏光镜(WSP)和可调光程的Savart偏光镜(MSP)的分束特性,得出WSP相较于SP具有更好的剪切能力和WSP可优化系统光路的结论.获得了不同楔形结构角下MSP的光程差、横向剪切量随楔形移动量的变化曲线.通过实验验证,获取了不同剪切量下的干涉图像和复色光下平行、垂直分量的空间图像,进而获得了总的强度图像和差分强度图像.得出差分强度图像相较于偏振强度图像具有较高对比度的结论.研究结果对双通道成像光谱系统的性能优化具有一定的参考意义.     

Polarization radio imaging of various objects in the millimeter-wave range

We present methods and results of radio imaging of various technical objects at a frequency of 94 GHz for vertical and horizontal polarizations. We analyze the features of the formation of polarization-difference images in the millimeter-wave range and the typical properties and methods of processing of such images. The influence of experimental conditions (noise level, antenna focusing, and imperfect knowledge of the directional pattern) on the quality of image reconstruction is numerically simulated. To increase the spatial resolution of images, we propose filtering of the spatial spectrum of a reconstructed image, which allows for its a priori statistical characteristics. Possibilities of passive polarization stereo imaging and a method of its realization in the millimeter-wave range are considered.     

正交偏振多光谱成像术应用于活体微循环观察研究

构建一种小型、简洁的活体微循环多光谱成像系统,将正交偏振光谱成像术OPS Imaging及液晶可调谐滤光片LCTF应用于活体微循环多光谱成像。LCTF具有较高的成像质量、较低的功耗、且没有移动部件和图像移动,能够连续、随机地在可见-近红外波段上快速实现波长的任意调谐。利用该系统,对活体裸鼠的耳廓采用检偏角为90°(正交偏振方式)与0°两种方式进行了试验,获取了裸鼠耳廓微血管的多光谱图,得出采用正交偏振成像方式的图像的对比度及图像细节均优于检偏角为0°时的图像。试验验证了正交偏振多光谱成像技术能增强活体微循环观察效果。     

Polarization Sensitive Spectral Interferometric Optical Coherence Tomography for Biological Samples

A spectral interferometric optical coherence tomography (OCT) system which has polarization sensitivity is developed. This system reduces the mechanical scanning dimension by employing the principle of spectral interferometry, and measures a two dimensional cross-sectional image of biological tissue with one dimensional mechanical scanning. Sixteen OCT images with different polarization conditions are measured, and two dimensional distributions of each element of the Müller matrix of a sample to be measured are calculated.     

伪装目标与背景的偏振对比特性

为解决传统光强探测手段难以有效探测和识别伪装目标这一难题,基于偏振探测技术搭建了光谱偏振探测成像系统,利用该系统在位于442.0,545.5,670.5,850.5 nm的窄波段对典型草地、土壤背景下的某型深绿色和土黄色伪装涂层进行了光谱偏振探测实验研究。并通过编制的图像处理软件对测试结果进行处理分析以提取其中的偏振信息,获得了目标与背景偏振度和偏振对比度随探测波长和探测角的变化规律。研究结果表明,合理地选择偏振成像探测条件可以使伪装涂层与背景之间存在较大的偏振对比度,可以实现对传统伪装涂层涂覆的目标的有效探测和识别。     

Phase-resolved functional optical coherence tomography: simultaneous imaging of in situ tissue structure, blood flow velocity, standard deviation, birefringence, and Stokes vectors in human skin

We describe a phase-resolved functional optical coherence tomography system that can simultaneously yieldin situ images of tissue structure, blood flow velocity, standard deviation, birefringence, and the Stokes vectors in human skin. Multifunctional images were obtained by processing of analytical interference fringe signals derived from two perpendicular polarization-detection channels. The blood flow velocity and standard deviation images were obtained by comparison of the phases from pairs of analytical signals in neighboring A-lines in the same polarization state. The analytical signals from two polarization-diversity detection channels were used to determine the four Stokes vectors for four reference polarization states. From the four Stokes vectors, the birefringence image, which is not sensitive to the orientation of the optical axis in the sample, was obtained. Multifunctional in situ images of a port wine stain birthmark in human skin are presented.     

Jones Matrix Imaging of Biological Samples Using Parallel-Detecting Polarization-Sensitive Fourier Domain Optical Coherence Tomography

A polarization-sensitive Fourier domain optical coherence tomography (PS-FD-OCT) system has been developed. By using a two-dimensional CCD camera, this PS-FD-OCT simultaneously obtains two spectral interferograms corresponding to orthogonal polarization components of a probing beam. FD-OCT avoids axial mechanical scanning, therefore, two OCT images are obtained by a single lateral scanning. This system requires only two one-dimensional scannings for determining the Müller matrix images of a sample. In the Müller matrix images, the birefringence properties of the inner surface of a porcine esophagus are revealed.     

Switchable Multi-Wavelength Erbium-Doped Fiber Lasers based on a Mach-Zehnder Interferometer Using a Twin-Core Fiber

A switchable multi-wavelength erbium-doped fiber ring laser based on a compact in-fiber Mach-Zehnder interferometer comb filter at room temperature is presented. The comb filter is formed by splicing a section of twin-core fiber between two single mode fibers. By adjusting the states of the polarization controller appropriately, the laser can be made to operate in stable single-, dual- and three-wavelength lasing states. The operation principle is based on spectral hole burning induced by the saturated effect and polarization hole burning.     

“Compact Spectral Imaging” System Using Liquid Crystal for Fast Measurement

The authors propose a compact system for measuring a multispectral image within a short observation time. This system consists of a lens array and a polarization interferometer. The interferometer has two wedge-shaped liquid crystal layers. Images of an object created by the lens array are modulated with variable optical path differences by the interferometer and detected simultaneously by an image sensor. From the detected images, we can reconstruct the spectral image of the object. Experimental results are presented.     

基于LCVR调谐的全偏振多谱段成像系统

提出一种新型全偏振多谱段成像系统,将液晶相位可变延迟器LCVR应用于全偏振成像技术,在可见-近红外波段上可快速实现光的全偏振态的精确调制.系统由光学镜头、LCVR、偏振片、滤波片和CCD探测器组成.文章首先介绍了系统结构、工作原理和光学设计,并提出了适合本系统的偏振定标方法,建立了偏振定标系统,实现了利用较小面积的偏振...     

通道调制型偏振成像系统的偏振参量重建

通道调制型偏振成像系统中,焦平面上获取的信息需要通过目标偏振参量的重建才能有效提取,因而重建是目标识别、材料分析、生物医疗等技术进一步应用的前提.为了实现在非理想情况下通道调制型偏振成像系统的偏振参量精确重建,需要解决成像系统中电荷耦合器件(CCD)采样频率与频谱位置偏移对重建的影响.本文首先详细分析了频谱不发生混叠的条件:CCD采样频率应至少为4倍基频;在偏振干涉频谱位置偏移时,使用最大频谱法确定各个偏振态的载波频率,通过频移、滤波和傅里叶变换获得目标的偏振重建二维图像;最后通过计算机模拟仿真与实验分析结合的方法验证该重建方案的可行性与有效性.模拟与实验结果表明:改进后的偏振重建法得到的偏振图像与原始输入图像的均方差在0.001以下,峰值信噪比有明显的提高,且结构相似度可达到0.9以上,表明该方法获得的二维偏振态重建图像精度高,与理论偏振解调法相比具有很大的优越性.该工作希望为后续偏振探测与分析进一步的研究提供参考.     

Observation of dressed excitonic states in a single quantum dot

We report the observation of dressed states of a quantum dot. The optically excited exciton and biexciton states of the quantum dot are coupled by a strong laser field and the resulting spectral signatures are measured using differential transmission of a probe field. We demonstrate that the anisotropic electron-hole exchange interaction induced splitting between the x- and y-polarized excitonic states can be completely erased by using the ac-Stark effect induced by the coupling field, without causing any appreciable broadening of the spectral lines. We also show that by varying the polarization and strength of a resonant coupling field, we can effectively change the polarization axis of the quantum dot.     

Polarization-Sensitive Spectral Interferometric Optical Coherence Tomography for Human Skin Imaging

Polarization-sensitive spectral interferometric optical coherence tomography (PS-SI-OCT) is designed for imaging of the inner structure of a biological tissue with polarization properties corresponding to Müller matrix elements. With arbitrary polarization state of incident and reference light, the change of polarization state can be acquired, and the axial structure of the tissue is measured by single detection of the power spectrum, superposition of object and reference light. Using with this OCT system, a cross-sectional Müller matrix images of human skin can be observed.     

基于声光滤光和液晶相位调谐的高光谱全偏振成像新技术

为了获取高光谱分辨率、高空间分辨率、高偏振精度、高信噪比和稳定性好的全部Stokes参量光谱图像, 考虑到声光可调谐滤光器(acousto-optical tunable filter, AOTF)的±1级衍射光的正交特性, 提出用一个AOTF滤光, 一个液晶可变延迟器(liquid crystal variable retarder, LCVR)进行相位调制和两个CCD相机分别对±1级衍射光成像的高光谱全偏振成像新技术. 从所采用的光学元件的穆勒矩阵出发, 阐述了该技术的基本工作原理; 理论分析表明, LCVR不但不会影响到第一个Stokes参量的探测精度, 而且后3个Stokes参量的相对误差分别优于0.064%, 0.31%和3.97%; 利用原理样机获取了450–700 nm、光谱带宽为10 nm的26个光谱通道的图像数据, 成像质量良好; 以工作波长为600 nm的入射光为例, 对其全部Stokes参量图像进行了具体分析讨论. 结果表明, 该新技术原理正确, 方案可行. 该研究可为光谱偏振成像技术提供新的理论和实现方案.     

All-optical image switch based on bacteriorhodopsin film

While two waves are coupled in bacteriorhodopsin (bR) film, a beam of incident light carrying the image is transferred to two diffraction beams whose intensities can increase from zero to a maximum and then decrease to a stable value with the increase of the writing time. Based on the relation among the polarization states of image in a recording beam and diffraction beams, we have proposed and demonstrated the all-optical image transfer switch which depends on the effective time and has the function that within the effective time, a polarization state image is automatically transferred to two images whose polarization states are perpendicular, and the transfer stops automatically beyond the effective time. A time-dependent all-optical image switch with muti-outputs is implemented.     

High-speed fiber based polarization-sensitive optical coherence tomography of in vivo human skin

A high-speed single-mode fiber-based polarization-sensitive optical coherence tomography (PS OCT) system was developed. With a polarization modulator, Stokes parameters of reflected flight for four input polarization states are measured as a function of depth. A phase modulator in the reference arm of a Michelson interferometer permits independent control of the axial scan rate and carrier frequency. In vivo PS OCT images of human skin are presented, showing subsurface structures that are not discernible in conventional OCT images. A phase retardation image in tissue is calculated based on the reflected Stokes parameters of the four input polarization states.     

Experimental observation and analysis of novel pulse properties in erbium-doped fiber ring laser with normal cavity dispersion

We demonstrate the experimental observation of different operation states in erbium-doped fiber ring laser with normal cavity dispersion. The Q-switching, Q-switching mode-locking (QML), continuous wave mode-locking (CML), harmonic mode-locking (HML), double-pulse and multiple-pulse operation states can be manipulated by only adjusting the polarization controller with the same pump power. The output spectral bandwidth and pulse width of operation states are measured. The central wavelength dynamics of different operation states achieved by adjusting the polarization controller are also observed and analyzed. It is shown that pulse width, polarization, chirp and stability of different operation states are diverse by using nonlinear polarization rotation technique.     

Polarization state and image rotation via spontaneously generated coherence in a spinning fast light medium

In this article we propose a four-level rubidium (Rb⁸⁷ ) atomic system for observing interesting features of polarization state rotation in a fast light medium. We investigate spontaneously generated coherence (SGC) for a spinning medium. We show how SGC can affect different spectral profiles of the polarization state and images in this suggested model. We observe a 0.5 radian rotation and 2.5 microsecond time advancement in our proposed system. Our precise results will provide a new platform for researchers in quantum optics due to its applications in image coding, telecommunications and cloaking technology.     

长波红外高光谱偏振特性的伪装目标识别方法

光谱偏振探测可以综合获得目标的光谱、强度、偏振态等参数，有利于改善对目标的探测和识别能力。本文介绍了基于红外高光谱偏振特性的伪装目标识别方法，搭建了长波红外高光谱偏振测量系统，开展了对两类伪装目标在不同温度下的高光谱偏振成像实验，获取了有效的实验数据并进行处理分析。结果表明：两类伪装目标即使涂覆相同的表面涂料，但受基底材料的热传导率影响, 在相同温度差异下红外偏振特性的提升量明显大于辐射亮度，并有着温差越大偏振特性提升量差异越大的规律，同时显示出波段选择性。利用两类伪装目标偏振特性提升量的差异，有效解决相同温度下伪装目标无法识别的难题。     

PMMA材料在线偏振和圆偏振光下的超连续光谱特性分析

飞秒激光在透明材料加工过程中会出现超连续光谱现象。在阐述超连续光谱产生的原理的基础上,为了分析PMMA材料在不同偏振光下产生的超连续光谱的阈值,设计了线偏光和圆偏光及不同能量加工PMMA材料的实验方案。利用光谱仪对产生的超连续光谱信号进行采集及处理,分析出不同能量下的线偏振(TE和TM)和圆偏振两种偏振态的超连续光谱的变化规律,并对比了相同能量下线偏振和圆偏振的超连续光谱的区别。实验中采用脉宽160 fs、中心波长为775 nm的飞秒激光,实验结果表明,同一偏振下能量越大,光谱谱宽越宽;通过对比不同能量下的光谱特性,观测出产生超连续光谱的阈值, 线偏振光的阈值为0.46 μJ,圆偏振光的阈值为0.586 μJ;对比相同能量下的线偏振和圆偏振光,线偏振的谱宽比圆偏振的宽。